2550x Trouble shooting

[Jaymz77]

I can borrow an oscilloscope from work, but I would need lessons in how to use it!
Even if I could use it, I wouldn't know how to interpret the results!
Might see if one of the guys who knows how to use it can help me...

I guess I'm glad someone else recognises I have an issue and I'm not just losing the plot!

[TIMBO]

Hey James stick with it, The circuit works well so it must be something simple.  Have you tried a patch lead or an FX pedal in the FX loop, just to rule out a JACK that's not switching right. Also check your wiring/components around this area.

The guys here http://www.guitargear.net.au/discussion/index.php are great might be able to point you in the right direction.

[Jaymz77]

Patch lead or no patch lead makes no difference.

Should the loop jacks be snitching jacks? I don't think the ones i used are

[SILVERGUN]

Hey Jaymz,
I'm not suggesting that a scope is the only way to fix your amp, but it is a great tool to actually see what the wave looks like as it passes through the different stages of your amp....That can be very helpful in narrowing down your problem......

-I would make sure that none of your capacitors are allowing DC to pass....you have to make sure that none of the coupling caps are allowing DC to get onto the grid of the next stage....
-If it were me,,,,I'd assume that I got something wrong in the LED, diode clipping area of the circuit, and I'd probably check over that about 20 times  
- Have you given us voltage measurements from each pin on each socket yet?

-There are so many possibilities for failure in an amp, that it is crazy to guess......voltages and scope traces don't lie

Check out this free book to learn more about troubleshooting with a scope....there is no better way to see inside your sound:
http://www.tubebooks.org/Books/intro_Middleton_troubleshooting.pdf

EDITED- The first link I gave you only contained a preview of the book....here's the full book:
http://www.tubebooks.org/Books/Middleton_troubleshooting.pdf

[Jaymz77]

Thanks heaps for that mate!

Ill check over the things you suggested this weekend. Might have to wait another week before i can get the scope, ill check today.

What makes you say the LED/ clipping circuit?

Cheers

[SILVERGUN]

What makes you say the LED/ clipping circuit?

Just the fact that there is a lot going on there....the schematic looks great until I look at that area and then,,,ehhh  
Not really what I want to see in a tube amp.....

[SILVERGUN]

Reading back over your thread now, it seems that I would be incorrect in looking at the clipping circuit, because it gets switched out when you are in the clean channel....
- Are you only experiencing this problem on the clean channel OR is it just easier to hear it without distortion?....I was unclear about this because we have shifted our focus a few times.....

I would strongly suggest to eliminate the ME-50 from the equation because it is adding a variable that we don't need.....the idea that it seems to help, is probably a result of the decreased signal strength

[Jaymz77]

I will try to confirm this over the weekend but I'm pretty sure it's a clean only issue. I will double check because there IS a shitload of distortion available in the lead channel that makes it hard to hear.

EXACTLY! That's what it sounds like: too much signal but with the ME-50 in the loop the signal is cut. The thing is, the 50 is supposed to be used up front, not through the loop. When it's through the loop the distortions are crap (too noisy) and the tuner function is all over the place due to the harmonics in the signal going through it.
The problem exists with no effects and with the effects up front. The only time it's fine is with the effects through the loop, but then the effects aren't great.

Thanks again

[SILVERGUN]

Try to forget about the ME-50 for now.....go right after the problem without the effects unit in there...
Also confirm/deny:
-Does it happen with the clean gain push/pull pot switched in one direction and not the other?

The area I have circled in this pic probably took a lot of heat to get soldered properly....heat could have damaged one/both of those diodes  
They appear to get switched in and out of the circuit by your clean gain pot/switch.

[Jaymz77]

Fair point.
There is another section near the LEDs that I was always concerned copped too much heat as well. I have some spare diodes so I might try replacing them one at a time and see how it goes.
The area I'm talking about is a junction of a white cap (the value I can't remember), the 2 LEDs and about 3 diodes.
Would I be able to put another diode in parallel to the existing ones (one at a time) to test? Or would I need to pull the existing ones?

[SILVERGUN]

There is another section near the LEDs that I was always concerned copped too much heat as well. I have some spare diodes so I might try replacing them one at a time and see how it goes.
The area I'm talking about is a junction of a white cap (the value I can't remember), the 2 LEDs and about 3 diodes.

That area is in the Distortion channel path, so if you're not having the problem on the Dist. channel (which we need to confirm/deny) then it wont help you

Would I be able to put another diode in parallel to the existing ones (one at a time) to test? Or would I need to pull the existing ones?

I would pull the existing ones...but only do the one's I circled first........try attaching the wire to the turret first by wrapping it around, solder that, and get all of that heat out of the way,,,then you'll only have to heat the cap and 2 diode leads to finish the joint

Definitely check if it is happening with the clean gain pot pulled AND pushed,,,or one or the other......first

[Jaymz77]

Sweet thanks mate.
I will try and report back

[Jaymz77]

Just a thought...
Are those diodes you circled only in the circuit when the rhythm clip mode is on, or are they there all the time in the clean channel regardless?

[TIMBO]

Hey James, Both of the clipping circuits are separate to the CLEAN path. The rhythm switch adds the (two diodes and .002) clipping to the clean path when the switch is on.

This rhythm sw. is a bit miss leading as it is a type of distortion so it may drop a bit of volume as well distort the playing.

BUT this does not explain why after playing a minute or so it kicks in other than a loose wire is shorting it into the circuit 

[Jaymz77]

I don't think it is cutting in.
Both the clipping circuits seem to be working fine (lead and clipped rhythm).
It's a different sound.

[SILVERGUN]

It's a different sound.

You're probably hearing the sound of a component failing....only problem is that some components don't just die, and that's it...they die slowly, or just live in an undead (but sick) state for awhile.
Diodes can fail in a couple different ways....short, open, leak, and these can be intermittent (which might explain why it comes and goes, or seems to happen intermittently)....that's why we want to rule out the diodes,,,especially because we already know that they took some heat.

Once we rule them out, we check them off our list and move forward...... a wise man once said "divide and conquer"

[Jaymz77]

Ok no worries.
I'll report back.

Thanks.

[Jaymz77]

Well the answer to the first question is no, it doesn't seem to be doing it on the lead channel.

[Jaymz77]

That diode bit of the circuit can't be the problem.
That is the rhythm clip diodes and the issue is there with them switched off.

[SILVERGUN]

the issue is there with them switched off.

Is it there with them switched on AND when they are switched off?....just curious

Are you working on getting us tube pin voltages?

You can try this and report back....
Take your guitar and plug it straight into your ME-50, and then plug the output of the ME-50 into the effects RETURN jack...
You will just be bypassing the preamp section of your amp, up to that point, and then if it doesn't act up, you'll know that your problem is probably before that point in the schematic (I'm guessing it is)

Until we get actual diagnostic tools involved, this is the only way to find a problem (divide and conquer)....poke around and hope to get lucky

[Jaymz77]

It's hard to tell, but I would say no. When you engage the rhythm clipping the volume drops a bit. With the clipping off, the problem exists with no volume drop.
I'll get pin voltages today

[Jaymz77]

Actually, I would say yes.
When the signal decays away, engaging the rhythm clipping makes the signal sound worse. So whatever the issue is it doesn't sound like it has anything to do with the clipping circuit.

It sounds to my uneducated ears like something is crapping out from too much signal. With the me50 in the loop, this cuts the signal a bit, cuts it just enough for the problem to go away.

[SILVERGUN]

It's hard to tell, but I would say no. When you engage the rhythm clipping the volume drops a bit. With the clipping off, the problem exists with no volume drop.

OK, I'm confused....let's get this straightnend out and then move forward 

When the signal decays away, engaging the rhythm clipping makes the signal sound worse. So whatever the issue is it doesn't sound like it has anything to do with the clipping circuit.

That statement kinda contradicts itself....this is how is sounds to me:
When I switch in the rhythm clipping, it makes it worse,,,,,but I don't think it has anything to do with the clipping circuit 


I'm not saying that you're problem is definitely in the clipping circuit, I'm just saying that we have to keep our answers very clear, so we're not on a wild goose chase.....I'll look harder at the schematic

[SILVERGUN]

OK, it appears to me that this small clean/rhythm clipping circuit consisting of 2 diodes and an .002 cap(whatever it does) IS in the circuit regardless of the switch being engaged or not....

The switch just re-routes the path and that affects the input signal strength into V2B grid

-With the switch open, the signal passes through the 10K and then the 100K (110K series resistance), and then the 47K and diodes/cap are the "grid leak path"

-With the switch closed, the signal sees the diodes/cap first as the "grid leak" and then the total series resistance of the grid stopper is reduced to approx. 33K due to the 47K being placed in parallel with the 110K series resistance.

[Jaymz77]

Sorry.
What I'm saying is that what you engage the clipping it sounds worse because the diodes are clipping a signal that is already damaged/ affected in some way, hence I don't think the diodes are the problem. It's like have 2 distortion pedals in series. The second one would be working with an already distorted signal. In this case the diodes are clipping a signal that already has issues.

Looking at my amp, those diodes  and cap are connected to signal ground at one end and the other goes back through the switch. So with that switch open, only the ground end is connected to anything

[Jaymz77]

I can see what you mean in the drawings, I better make sure I'm wired that way

[Jaymz77]

HOLD THE PHONE!!!!

Ive just noticed i have a resistor missing!!!! What an idiot.
That 47k resistor from the diodes back to V2.

Geez, how did i miss that? Ill chuck one in and report back!

[TIMBO]

Hi guys, SG your doing a great job. I am sure it is something simple.  

There is not a lot of components in the CLEAN signal path  and some can be removed as they are a tone/fizz control.

I marked a couple of bits that can be removed/changed that I think could be a problem......

Remove 1 - .047 cap
Remove 2 - 47p cap
Change 3 - .033 to .022 cap
Remove 4 - 470p cap
Remove 5 - .001 cap

If this problem DOES NOT present itself when in LEAD mode, the components marked :-

A - 220k
B - .022
C - 220k
D - 110K (220k II)
E - 47k
F - 1M
Are in the clean signal path and need to be checked for value and connection

Hope this helps.

[Jaymz77]

What program do i need to open that Timbo?

[SILVERGUN]

Hi guys, SG your doing a great job. I am sure it is something simple.

Thanks TIMBO 

What program do i need to open that Timbo?

Express SCH...it comes bundled with Express PCB       
 http://www.expresspcb.com/

BUT, WAIT!
Did you put the 47K in there?....and then double check that you've got the signal path wired correctly coming off of the pot/switch?

[Jaymz77]

I just put the missing resistor in.
Im double checking the wiring of the switch now. (i keep saying switch because i didn't use pull pots, i used regular pots with separate switches)

[Jaymz77]

Any chance someone could pdf that for me?


Well i don't think the resistor is the answer, i think the problem is still there.
Im just letting the tubes cool now, then ill confirm

[TIMBO]

 

[SILVERGUN]

I'm not gonna have easy access to the forum for a while tonight....

Good luck Jaymz,,,,and at least we fixed one problem

TIMBO....TAG---you're it 

[Jaymz77]

Thanks Timbo. I had E missing!

Well, i have been playing through the amp for a while now and my observations are...

* Amp seems more consistent. IE things seem to be behaving a little more predictably, with and without effects.
* The tone seems more consistent across different volume:gain ratios
* Things don't seem to be intermittent anymore (to be confirmed) i seem to have control over everything.
* That buzzy sort of distortion seems to be still there but it seems to be controllable. If i dial the gain right up it is very buzzy like before, but if i wind the gain back to 8 or 9 it seems to tame it substantially. However if i run my ME-50 through it (up front like its supposed to be used) using only compressor and a touch of reverb, this also seems to tidy the buzziness up a fair bit too.
* Buzziness seems to go away with rhythm clipping engaged.
* Amp seems to have less noise
* This time the ME-50 sounds much closer when its plugged up front or in the loop. Through the loop still sounds a bit warmer, but this time instead of being much quieter it is actually a bit louder. Running through the loop also means certain thing on the ME-50 work a bit better (compressor, delay, chorus) but the fact that the compressor has more effect means that i have to wind the level up to match the dry signal level and this induces more noise.
I think this time around i prefer the ME-50 up front. I just can't quite get the same warmth from the compressor with it up front, less noise though.


Given this new found controllability (using the amp controls alone as well as in conjunction with the ME-50) and the fact that the buzziness seems to go away with the rhythm clipping engaged, I'm starting to wonder if that is how it is  supposed to be. Not having a real Jubilee to compare to to makes it hard.
Obviously there was SOME issue going on there (besides idiot me forgetting a resistor) but whether or not that is completely solved or not remains to be seen.

The next thing i will do is try another guitar. All this so far has been with my 62 reissue Strat with Seymour Duncan SSL-1 pickups. Ill try my Les Paul standard and see how that goes.

[Jaymz77]

AND THANKS HEAPS FOR ALL YOUR HELP SO FAR SILVERGUN!!!!!

[Jaymz77]

Ok.
I just tried my Les Paul through it and its buzzy as all hell. It fact it is hard to get a clean clean at all. I had to have the gain down below 9 o'clock to get a clean tone.
Again, i don't know if this would be deemed as normal or what, but the type of buzziness I'm getting just doesn't sound right to me. It doesn't sound like typical marshall overdrive to me. It sounds buzzy/ fuzzy.

[Jaymz77]

Well after poking around a little i can tell you that removing the 47pf at V1 (number 1 in Timbos drawing) makes the buzzy/ fuzzy/ fizziness worse.
Ill be putting that back in...

[Jaymz77]

*CORRECTION* - Number 2 on Timbos drawing

[TIMBO]

That 47pf could be increased up to about 250Pf.

[Jaymz77]

I was wondering if increasing that value would change anything given removing it makes it worse.
Funny though, when people talk about upgrading their jubilee to the newer revision of the circuit, that cap is removed.

Would you describe the overdrive as fuzzy, TIMBO? I'm mean on the rhythm channel with the clipping off and with the gain above 3 o'clock.

[SILVERGUN]

Even though you found the missing resistor and replaced it, did you ever replace the diodes that we talked about earlier?

They "could" still be contributing to the fizziness if they are failing....

AND THANKS HEAPS FOR ALL YOUR HELP SO FAR SILVERGUN!!!!!

You're very welcome Jaymz...it can be difficult to keep communication clear, and that is my main goal when trying to help someone...
There is a very systematic approach to troubleshooting that involves eliminating all potential problems until you have zero problems to eliminate.

Your problem stood out to me as a signal loss issue, and I chose to focus on an area of the schematic that "might" have something to do with that,,,,and combined with your pictures, I think we are onto something.....
The fact that we got lucky and you found a missing resistor is one victory,,,,but if you missed a resistor,,,there could be more..
You definitely "could have" overheated those diodes while soldering.....it could save you some time "guessing" if you just go in and replace them,,,,and in turn, rule them in OR out.

Good luck mate,
It can be very frustrating to try,,, but very rewarding to succeed....
 

[Jaymz77]

Will do.
I'll get those pin voltages too.

[TIMBO]

Hey James, This is a clip http://www.el34world.com/Forum/index.php?topic=15881.0 with a PL with P90s. This is the clean gain at about 8 and the rhythm switch on.

It could be a bit fuzzy and buzzy with humbuckers, so knock the volume back on your guitar till it cleans up and see how that goes.

[Jaymz77]

Thanks for that Timbo, nice amp.

I can definitely report though that there is something else going on with mine and its not those diodes Silvergun.
I just changed the diodes, making sure not to put too much heat into them, and it still has that buzzy/ fuzziness that I'm sure is not supposed to be there, least of all with a Strat. The signal gradually decays away into buzziness.
While i was in there i changed the diodes in the bias circuit, Not for any other reason but peace of mind, now i know they are ok too.

The amp does sound a little different (i don't think I'm imagining it) since the diode change, but it has done nothing for the problem. I guess there is a possibility that they might have been contributing because until the signal decays into buzziness it sounds damn good.
The other thing i noticed is that the point on the gain pot where the buzziness starts seems to be a bit higher... maybe an increment or so. Again, i don think I'm imagining it.

So, why do those more knowledgeable than me think i should look at next?
(and i haven't forgotten those pin voltages)

[Jaymz77]

Pin voltages to ground are as follows (amp idle no input)

       V1     V2     V3     V4     V5
p1   237   222    249    0       0
p2   0       0        0       0       0
p3   2       1        44     438   442
p4   0       0        0       433   433
p5   0       0        0       -36    -36
p6   215   159    235    0       0
p7   0       0        28     0       0
p8   1       0        44     0       0
p9   0       0        0


Let me know if you need more info.

[TIMBO]

Hey James , Those voltage are a close match to mine so there is nothing that the voltages are causing

Can you try a lower gain tube in V1 like a 12AT7 or AY7???

[Jaymz77]

Unfortunately I don't have spare tubes of any kind.
It just seems so weird that it happens over time.

[SILVERGUN]

It just seems so weird that it happens over time.

time = heat up = component failure

count how many components are in your amp -  subtract from that the number of components that you have ruled out = the amount of components you still have to rule out  

[SILVERGUN]

When you list pin 8 on V2  as having 0 volts, does that mean ZERO?....or is it more like  0.7-0.9 Vdc?